Mammalian protein kinases are important regulators of cellular functions. Because disfunctions in protein kinase activity have been associated with several diseases and disorders, protein kinases are targets for drug development. The Tyrosine kinase family, and particularly the subset of receptor tyrosine kinases, is enriched with proven and putative cancer targets. Receptor tyrosine kinases (RTKs) such as EGFR, HER2, KIT and KDR are well characterized proteins with a clearly established role in cancer. Drugs targeting these RTKs, such as Gleevec, Iressa, and Tarceva, have been approved for the treatment of certain cancers. Other RTKs are less well characterized but have also been implicated in cancer. For example, emerging data suggests that inhibitors of TRKC, ROS, CSF1R/FMS and ALK may be useful in the treatment of cancer. MET and RON are two particularly attractive RTK targets for the development of new agents to treat cancer.
Hepatocyte growth factor (HGF), also known as scatter factor, is a multi-functional growth factor that enhances transformation and tumor development by inducing mitogenesis and cell motility. Further, HGF promotes metastasis by stimulating cell motility and invasion through various signaling pathways. In order to produce cellular effects, HGF must bind to its receptor, MET, a receptor tyrosine kinase. MET, a widely expressed heterodimeric protein comprising of a 50 kilodalton (kDa)α-subunit and a 145 kDa β-subunit (Maggiora et al., J. Cell Physiol., 173:183-186, 1997), is overexpressed in a significant percentage of human cancers and is amplified during the transition between primary tumors and metastasis. The various cancers in which MET overexpression is implicated include, but are not limited to, gastric adenocarcinoma, renal cancer, small cell lung carcinoma, colorectal cancer, prostate cancer, brain cancer, liver cancer, pancreatic cancer, and breast cancer. MET is also implicated in atherosclerosis and lung fibrosis.
MET was first identified as a transforming DNA rearrangement (TPR-MET) in a human osteosarcoma cell line that had been treated with N-methyl-N′-nitro-nitrosoguanidine (Cooper et al. 1984). The MET receptor tyrosine kinase (also known as hepatocyte growth factor receptor, HGFR, MET or c-Met) and its ligand hepatocyte growth factor (“HGF”) have numerous biological activities including the stimulation of proliferation, survival, differentiation and morphogenesis, branching tubulogenesis, cell motility and invasive growth. Pathologically, MET has been implicated in the growth, invasion and metastasis of many different forms of cancer including kidney cancer, gastric cancer, lung cancer, ovarian cancer, liver cancer and breast cancer. Somatic, activating mutations in MET have been found in human carcinoma metastases and in sporadic cancers such as papillary renal cell carcinoma. There is also evidence the MET signaling pathway can play an important role in resistance to cancer therapies. For example, the MET gene has been found to be amplified in lung cancer patients that have relapsed after initial response to EGFR inhibitors such as gefitinib and erlotininb. In addition to cancer there is evidence that MET inhibition may have value in the treatment of various indications including: Listeria invasion, osteolysis associated with multiple myeloma, malaria infection, diabetic retinopathies, psoriasis, and arthritis. Mutations in the MET coding sequence are relatively uncommon in human cancers. However, based on the precedent of the selection of BCR-ABL mutations in chronic myelogenous leukemia patients treated with imatinib and EGFR mutations in cancer patients treated with erlotinib and gefitinib, these and/or perhaps additional MET mutations that might confer drug resistance are predicted to become increasingly prevalent if MET inhibitors become widely use in cancer. Therefore drugs that effectively inhibit some of these MET mutations could become very important tools in future cancer therapies.
MET is closely related to a group of five receptor tyrosine kinases which have not been as thoroughly studied as MET itself. These include Tyro3/Sky, MER, AXL, RYK and RON. The tyrosine kinase RON is the receptor for the macrophage stimulating protein and is the closest relative of MET, belonging to the MET family of receptor tyrosine kinases. Like MET, RON is implicated in growth, invasion and metastasis of several different forms of cancer including colorectal cancer and bladder cancer. There is also evidence that deregulated AXL and MER can play important roles in cancer. MER has many properties consistent with activity as an oncogene. Transgenic mice expressing MER in the hematopoietic lineage develop symptoms similar to T-cell lymphoblastic leukemia/lymphoma and it is expressed in most T cell acute lymphoblastic leukemia (T-ALL) patients. Studies in mouse models suggested that AXL is important for the growth of breast cancer where AXL appeared to regulate both angiogenic and tumorigenic processes. Additional studies with human cancer cell lines suggest that AXL is involved in NSCLC metastasis and drug resistance. Although very little is known of the normal and pathological roles of Tyro3/Sky this receptor tyrosine kinase shares certain properties and functions with its better studied relatives and may also eventually prove to have an important role in cancer. RYK is also expressed in certain cancers but it is an atypical orphan receptor tyrosine kinase that lacks detectable kinase activity and thus its tractability as a target for small molecule cancer therapeutics is currently uncertain.
Because kinases have been implicated in numerous diseases and conditions, such as cancer, there is a need to develop new and potent protein kinase inhibitors that can be used for treatment. The present invention fulfills these and other needs in the art. Although certain protein kinases are specifically named herein, the present invention is not limited to inhibitors of these kinases, and, includes, within its scope, inhibitors of related protein kinases, and inhibitors of homologous proteins.